/*
 * Copyright 2022 Deep Learning on Flink Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.flinkextended.flink.ml.data.impl;

import org.flinkextended.flink.ml.cluster.node.MLContext;
import org.flinkextended.flink.ml.data.RecordReader;
import org.flinkextended.flink.ml.util.SpscOffHeapQueue;

import java.io.DataInputStream;
import java.io.EOFException;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;

/** a simple RecordReader implement. */
public class RecordReaderImpl implements RecordReader {

    private final DataInputStream input;
    private boolean eof = false;

    public RecordReaderImpl(MLContext mlContext) {
        SpscOffHeapQueue.QueueInputStream in = mlContext.getInReader();
        this.input = new DataInputStream(in);
    }

    public byte[] tryRead() throws IOException {
        if (input.available() > 0) {
            return read();
        }
        return null;
    }

    public boolean isReachEOF() {
        return eof;
    }

    public byte[] read() throws IOException {
        /** Record format: uint32 length byte data[length] */
        byte[] lenBytes = new byte[4];
        int lenRead;
        try {
            // Only catch EOF here, other case means corrupted file
            lenRead = input.read(lenBytes);
            if (lenRead < 0) {
                eof = true;
                return null;
            }
        } catch (EOFException eofException) {
            eof = true;
            return null; // return null means EOF
        }
        if (lenRead < lenBytes.length) {
            input.readFully(lenBytes, lenRead, lenBytes.length - lenRead);
        }
        long len = fromInt32LE(lenBytes);

        byte[] data = new byte[(int) len];
        input.readFully(data);
        return data;
    }

    private int fromInt32LE(byte[] data) {
        assert data.length == 4;
        ByteBuffer bb = ByteBuffer.wrap(data);
        bb.order(ByteOrder.LITTLE_ENDIAN);
        return bb.getInt();
    }

    @Override
    public void close() throws IOException {}
}
